The present invention relates to modular contact systems such as those use in cable heads for telephone distributor frames, and in particular, to a protection and monitoring device for protecting such systems against external voltage surges, e.g.: lightning, inducted signals from railway lines, line-conveyed disturbances, electromagnetic impulses (e.g. nuclear explosions), etc.
A cable head, which is a typical example of a modular system and which is used below as a specific example of such a modular system, provides both test and protection functions. Such a modular contact system comprises a series of contacts each constituted by two blades of flexible metal pressing resiliently against each other. The connection may be opened by sliding a thin flat insulator element between the contacting blades, and various test, measurement, or protection circuits may be inserted in series by inserting a thin flat element having two independent contact surfaces for making contact with the blades. In particular, lightning protectors may be inserted in series. Cable heads and other systems such as connection strips are designed to receive particular corresponding lightning protectors, fuses, or other protection components (such as varistors). The housing which receives the components is designed as a function of the components it is to receive. The components selected thus determine the configuration of a particular housing. In particular, if a lightning protector is to be changed, for example to switch over from two-pole protection to three-pole protection, then the housing needs changing as well, and that is expensive.
With three-pole protection, any surge voltage between one of the phases or conductors of a component and ground or the other phase causes a short circuit to be established both to ground and between the phases.
The phenomena involved in providing such protection are not well understood because they are rapid, destructive, and difficult to reproduce in the laboratory under realistic conditions. If the contact system was designed as a transformable or adaptable support, various experiments could be performed without having to change the system or use a different one.